Mechanical behavior of quenched isotactic polypropylene crystallized by thermal and solvent treatments

Films of quenched isotactic polypropylene were either annealed at 80, 90, 100, 110°C for 30 min or kept in different liquids for 24 h at 25°C. The liquids were cyclohexane, chloroform, and carbon tetrachloride. Both treatments induce crystallization of quenched films and the development of crystallinity was detected by carrying out density and wide-angle x-ray scattering measurements. Small-angle light scattering experiments, performed on the starting and on the crystallized samples, show that in the zones in which spherulites are present the basic gross morphology does not change after the treatments, although the increase of crystallinity is substantial for all the samples. The analysis of the mechanical behavior also indicates the absence of relevant morphological changes following the different treatments. On the other hand the increased crystallinity strongly influences the complex structural and molecular rearrangement characterizing the transition from the spherulitic to the fiber morphology. The results are discussed in terms of the great significance that structural modifications have on the physical properties.